thanks for fixing a very stupid decision by Mozilla. Still, I should not need an extension to have a basic functionality like this!!

THANK YOU! This option should have never been removed from Firefox.

Although this feels like it should really be an about:config option, this extension is simple and effective, and very easy to verify as safe for the paranoid that want to peek inside.

The only issue I noticed is that you might occasionally encounter a 403 error or the like on sites that block hotlinking (I'm guessing the native function didn't actually reload the image). Aside from that functionality appears to be identical to the old context menu item.